In an examination, a student scores 4 marks for every correct answer and loses 1 mark for every wrong answer. If he attempts all 80 questions and secures 120 marks, How many questions does he answer correctly?
30
60
50
40
Explanation:
Let the number of correct answers be x
Then, number of wrong answers = $\left(80 - x\right)$
4x – $\left(80 - x\right)$ = 120
=> 4x – 80 + x = 120
=> 5x = 200
=> x = 200/5 = 40
i.e., he does 40 questions correctly